Sensor for magnetoencephalography meter and supermultichannel magnetoencephalography meter system using the same

ABSTRACT

This invention relates to a super-multichannel MEG system comprising sensors produced by printing sensor coils on thin films in positions shifted from each other and by laminating multiple thin-film sensor coils together. Intended for use in a multichannel MEG system comprising a dewar, the sensors are arrayed in the dewar to detect biomagnetism and the Superconducting QUantum Interference Devices (SQUIDs) to detect signals coming from the sensors. These sensors are characterized by the sensor coils being printed on thin films in positions shifted from each other laterally and longitudinally and by their being laminated in the required number.

TECHNICAL FIELD

This invention relates to a super-multichannel magnetoencephalographysystem used to take measurements of the magnetic fields generated in thebrains of the subjects. Specifically, it relates to a super-multichannelmagnetoencephalography system that is characterized by the structure ofthe sensors arrayed to surround the head of the subject.

BACKGROUND OF THE INVENTION

The human brain generates electric signals. These signals are very weak,but can be measured non-invasively by various methods. One of suchmethod is the biomagnetism-measuring method which is used to measure themagnetic field on the outer surface of the head created by electriccurrents in the brain.

A magnetoencephalography (MEG) system (hereinafter referred to as theMEG system) is a specially improved, highly sensitive device fordetecting magnetic fields, and comprises magnetic field sensors,detectors for the currents flowing through the sensors, and relatedelectronic units. The MEG system has much potential as a non-invasivedevice for measuring brain functions because it has high time and spaceresolutions.

The magnetic field sensors of a planar type used in such a systemtypically comprise electric wires in the shape of multi-loop coils thatcreate minute electric currents when they are penetrated by a magneticflux. For example, as shown in FIG. 3, a sensor comprises a coil (a) forthe magnetometer, and two directional derivative coils (b) and (c) forthe gradiometer that detects the direction of magnetic field gradient.These three coils, (a), (b), and (c), are combined, overlaid, andintegrated with each other to obtain a multi-layer laminate. Sensors,without coil (a) but comprising the coils (b) and (c) are in common use.Also, sensors using only the coil (a) are also available.

Each sensor coil is required to have a surface area of a few squarecentimeters for the coil to have enough sensitivity in theabove-described system. If sensor coils requiring such an area werearrayed closely on the surface of the head, the number of coils wouldhave to be limited, as shown in FIG. 2, with the upper limit beingseveral hundreds of channels at the largest.

One objective of this invention is to create a super-multichannel MEGsystem capable of very high resolutions ranging from several hundreds toseveral tens of thousands of magnifications, with said system comprisingsensors characterized by the sensor coils being printed on thin films inpositions shifted from each other laterally and longitudinally by alength of {a}/{n} and the sensor coils being laminated in a number of{n}² sheets where {a} is the length of a side of the thin-film coil, and{n} is a natural number, and wherein the signals coming from manycorresponding thin-film sensors are sent in parallel with each other,and are switched over by the input unit of eachmultichannel-Superconducting QUantum Interference Device (SQUID).

Another objective of this invention is to create a super-multichannelMEG system capable of very high resolutions wherein the sensors areproduced as described above by printing sensor coils on thin films inpositions shifted from each other laterally and longitudinally by alength of a/n and laminating {n}² sheets of thin-film coils, and whereina multiple number of such sensors are arrayed longitudinally andend-to-end, while aligning them accurately, to make it possible todetect the difference in electric currents generated by thecorresponding coils and to measure the primary derivative or thehigh-order derivative in the axial direction of the magnetic field.

DISCLOSURE OF THE INVENTION

The means adopted by this invention to solve the above-describedtechnical problem and to achieve the above-described objectivescomprises the sensors, which are used in the magnetoencephalometer,according to claim 1, and are characterized by the sensor coils beingprinted on thin films in positions shifted from each other laterally andlongitudinally and by the sensors being laminated in the required numberof sheets.

Another means of implementing this invention comprises the sensors,which are used in the magnetoencephalometer and are characterized by thesensor coils being printed on thin films in positions shifted from eachother laterally and longitudinally by a length of {a}/{n}, and by thesensors being laminated in a number of {a}² sheets where {a} is thelength of a side of the thin-film coil, and {n} is a natural number.

Another means of implementing this invention comprises the sensors,which are used in the magnetoencephalometer and are characterized by theabove-described sensors comprising laminated sensor coils being arrayedlongitudinally and end-to-end, while aligning them accurately, to makeit possible to detect the difference in electric currents generated bythe corresponding coils and to measure the primary derivative or thehigh-order derivative in the axial direction of the magnetic field.

Another means of implementing this invention comprises asuper-multichannel MEG system characterized by this system comprisingthe above-described sensors, high-speed switching means corresponding toeach coil in the sensor, and SQUIDs arrayed correspondingly with thehigh-speed switching means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram that explains the configuration of the sensors ofthis invention.

FIG. 2 is a schematic diagram showing the layout of sensors on the head.

FIGS. 3( a), 3(b) and 3(c) show some examples of sensor coils of theconventional planar type.

PREFERRED EMBODIMENT OF THE INVENTION

This invention is further described with respect to its preferredembodiment of the super-multichannel MEG system, while referring to thedrawings in which FIG. 1 is an explanatory diagram showing the sensorcoils used in this MEG system.

In FIG. 1, sensors 1 comprises thin-film coils having the same functionas conventional sensor coils of the planar type, but the coils in thisinvention are printed in positions shifted in the lateral andlongitudinal directions precisely by a length of {a}/{a}, and the sensorcoils are laminated in the number of {n}², where {a} is the length of aside of thin-film coil, and {n} is a natural number. A coil printed onthin film has a thickness of several μm. Even if several hundreds toseveral thousands of coil sheets were laminated, the sensor would have amaximum thickness of only several millimeters. Precise lamination can beeasily achieved using contemporary technology.

As shown in FIG. 2, a multiple number of the sensors 1 are arrayed onthe head. The sensor coils 2 of each sensor 1 are connected to acorresponding SQUID 4, as in a conventional system, by way of acorresponding switching means 3, such as a multiplexer. Thus, when themultiplexer is switched over, one by one, from 1 to {n}², a measuringsystem having as many as several tens of thousands of magnifications canbe configured, using the numbers of SQUIDs and amplifiers similar tothose used in conventional technology. As regards the units downstreamof the SQUIDs, a conventional system is used as is. These sensors arearrayed longitudinally, and the difference in electric currentsgenerated by the corresponding coils is obtained to measure the primaryderivative or the high-order derivative in the axial direction of themagnetic field. Thus, the gradiometer in the axial direction can beconfigured. In this manner, it is possible to set up a system capable ofobtaining ultrahigh resolutions merely by using thin-film technology tomultiplex the sensors while making use of a configuration similar toexisting electronic systems.

A major aspect of a system having the above-described configuration isthat a super-multichannel system can be built at a lower cost with noneed to prepare large electronic circuits downstream of the SQUIDs. Thiscan be done when the output from the i-th layer is switched by ahigh-speed switching means so that the output can be electronicallycombined at the same time at the multichannel SQUID. Since the signalcomponents measured by the MEG meter are only several hundreds of Hz,this switching operation can be performed at a full speed, ensuringsynchronized measurements.

With this system, the information detected by a sensor is determined byits number of laminated coils. In large laminates, the number of sensorcoils increase with an increase in the number of laminated sheets evenwhen there is no change in the number of sensors arrayed on the head.Information is collected in amounts much larger than the amountscollected by conventional sensor coils. Therefore, it is possible to setup a system having ultrahigh resolutions ranging from several hundredsto several tens of thousands of magnifications as compared toconventional systems.

The preferred embodiment of the sensors according to this invention hasbeen described above. However, it is to be understood that the mostfeasible method and equipment have been explained simply to describe theembodiment of this invention. For example, the length of {a}/{n} inwhich the sensors are shifted need not be always constant, and thelamination need not be in the number of {n}², because it is alsopossible to obtain the same result if the output data from the abovelaminated sensor coils are processed using adequate software.Furthermore, the planar type of sensor coil is not limited to the squareshape, but the sensor coils may have other shapes. The above embodimentof this invention has been described for the sensors of the planar type.However, the conventional gradiometer or the high-order derivativesensors can also be configured by arraying multiple sensorslongitudinally and end-to-end, while aligning the laminated sensorsaccurately. The sensors can be connected to the SQUIDs by way of theswitching means to set up an MEG system. These sensors need not beplaced on the head laterally, but may be placed vertically to measurethe magnetic field components that are parallel to the head. Anappropriate switching means of contemporary technology can be utilizedfor this invention.

Any other embodiments of this invention can be implemented withoutdeparting from the spirit of this invention and its majorcharacteristics. Therefore, the above-described embodiment of thisinvention is merely for explanatory purposes in all respects and shouldnot be construed as limiting.

INDUSTRIAL APPLICABILITY

Each of the sensors according to this invention comprises sensor coilsthat are printed on thin films in positions shifted from each other atcertain lateral and longitudinal directions and are laminated together.The signals coming from multiple thin-film sensor coils are sent inparallel and switched over by the input units of the multichannelSQUIDs. By adopting such switching means, it is possible to obtain ahigh-resolution system that has resolutions ranging from severalhundreds to several tens of thousands of magnifications, as comparedwith conventional systems.

1. A sensor unit for use in a magnetoencephalometer, the unitcomprising: a plurality of sensor, each of which comprises a film and asensor coil printed thereon, each of the sensor coils is arranged in aposition shifted from one another laterally and longitudinally and islaminated in an overlapped manner, wherein each of the sensor coilssenses signals at a different sensing position of an object to bemeasured, wherein said sensor coils are shifted in positions preciselyby a length of {a}/{n} in the lateral and longitudinal directions andare laminated together in the number of {n}², and wherein {a} is thelength of a side of the sensor coil, and {n} is a natural number.
 2. Thesensor unit of claim 1, wherein the plurality of sensors are configuredto detect the difference in electric currents generated by thecorresponding sensor coils and to measure the primary derivative or thehigh-order derivative in the axial direction of the magnetic field. 3.The sensor unit of claim 2, further comprising: high-speed switchingcorresponding to each said sensor coil in the sensor, andsuperconducting quantum interference devices arranged to correspond withthe high-speed switching.
 4. The sensor unit of claim 1, furthercomprising: high-speed switching corresponding to each said sensor coilin the sensor, and superconducting quantum interference devicesconfigured to correspond with the high-speed switching.